How to popup instead of echo - php

Question

I have created a contact form using HTML and PHP.
Right now when a user submit the contact form he redirect to a new page with the echo message, instead, I want this message to appears in a small popup window.
HTML Code:
<form action="/assets/bootstrap/php/emailscript.php" method="post">
<input type="text" placeholder="Name" name="Name" oninvalid="setCustomValidity('Please enter your name')"
onchange="try{setCustomValidity('')}catch(e){}" required >
<input type="text" placeholder="Company" name="Company" oninvalid="setCustomValidity('Please enter your Company name')"
onchange="try{setCustomValidity('')}catch(e){}" required >
<input type="text" placeholder="Email" name="Email" required pattern="[a-z0-9._%+-]+#[a-z0-9.-]+\.[a-z]{2,3}$" oninvalid="setCustomValidity('Please enter a valid e-mail address')"
onchange="try{setCustomValidity('')}catch(e){}" >
<input type="text" placeholder="Subject" name="Subject" oninvalid="setCustomValidity('Please enter a Subject')"
onchange="try{setCustomValidity('')}catch(e){}" required >
<textarea rows="5" placeholder="Message" name="Message" oninvalid="setCustomValidity('Please Write your Message')"
onchange="try{setCustomValidity('')}catch(e){}" required ></textarea>
<button type="submit" class="btn btn-primary"><i class="fa fa-paper-plane"></i> Send</button>
</form>
</div>
</div>
</div>
PHP Code:
<?php
if(isset($_POST['Name']))
{
$name=$_POST['Name'] ;
$company=$_POST['Company'] ;
$from=$_POST['Email'] ;
$message=$_POST['Message'] ;
$to="contact#website.com" ;
$subject="Website contact form";
$headers .= 'From: '.$name.' | '.$company.' | '.$from.' ' . "\r\n";
mail ($to, $subject, $message, $headers ) ;
echo "Your Email has bean sent.";
}
?>
Thanks